If you did not come right and are in a bind I wrote a small python script to extract all points of a single code (e.g. code 20) and put them in a new file. If you have python installed you can run the file from the command line. Extract the attached zip and run the file with python like this:
py extract20.py "input file path" "output file path" code
For example " py extract20.py sample.txt sample20.txt 20" will extract all code 20s from sample.txt and put them in sample20.txt
Note, use quotations around the paths if your paths have spaces in them.
Use at your own risk. There is minimal error checking and I did not test it on a large file like the 2GB file, but it reads and writes straight from and to the files, so hopefully there should not be any "insufficient memory" errors.
I do suggest that you try to use one of the approaches mentioned by other people though, such as QGIS, LASZIP or Cloud Compare. That will give you flexibility in future to handle different file formats/contents.
